1. Fall 2009COSC 6501 Welcome to COSC650 Towson University Yanggon Kim

2. Fall 2009COSC 6502 Introduction Outline Statistical Multiplexing Inter-Process Communication Network Architecture Performance Metrics Implementation Issues

3. Fall 2009COSC 6503 Building Blocks Nodes: PC, special-purpose hardware… –hosts –switches Links: coax cable, optical fiber… –point-to-point –multiple access …

4. Fall 2009COSC 6504 Switched Networks –two or more nodes connected by a link, or –two or more networks connected by a node A network can be defined recursively as...

5. Fall 2009COSC 6505 Strategies Circuit switching: carry bit streams –original telephone network Packet switching: store-and-forward messages –Internet

6. Fall 2009COSC 6506 Addressing and Routing Address: byte-string that identifies a node –usually unique Routing: process of forwarding messages to the destination node based on its address Types of addresses –unicast: node-specific –broadcast: all nodes on the network –multicast: some subset of nodes on the network

7. Fall 2009COSC 6507 Multiplexing Time-Division Multiplexing (TDM) Frequency-Division Multiplexing (FDM) L1 L2 L3 R1 R2 R3 Switch 1Switch 2

8. Fall 2009COSC 6508 Statistical Multiplexing On-demand time-division Schedule link on a per-packet basis Packets from different sources interleaved on link Buffer packets that are contending for the link Buffer (queue) overflow is called congestion …

9. Fall 2009COSC 6509 Inter-Process Communication Turn host-to-host connectivity into process-to-process communication. Fill gap between what applications expect and what the underlying technology provides. Host Application Host Application Host Channel

10. Fall 2009COSC 65010 IPC Abstractions Request/Reply –distributed file systems –digital libraries (web) Stream-Based –video: sequence of frames 1/4 NTSC = 352 x 240 pixels (352 x 240 x 24)/8=247.5KB 30 fps = 7500KBps = 60Mbps –video applications on-demand video video conferencing

11. Fall 2009COSC 65011 What Goes Wrong in the Network? Bit-level errors (electrical interference) Packet-level errors (congestion) Link and node failures Packets are delayed Packets are deliver out-of-order Third parties eavesdrop

12. Fall 2009COSC 65012 Layering Use abstractions to hide complexity Abstraction naturally lead to layering Alternative abstractions at each layer Request/reply channel Message stream channel Application programs Hardware Host-to-host connectivity

13. Fall 2009COSC 65013 Protocols Building blocks of a network architecture Each protocol object has two different interfaces –service interface: operations on this protocol –peer-to-peer interface: messages exchanged with peer Term “protocol” is overloaded –specification of peer-to-peer interface –module that implements this interface

14. Fall 2009COSC 65014 Host 1 Protocol Host 2 Protocol High-level object High-level object Service interface Peer-to-peer interface Interfaces

15. Fall 2009COSC 65015 Protocol Machinery Protocol Graph –most peer-to-peer communication is indirect –peer-to-peer is direct only at hardware level File application Digital library application Video application RRPMSP HHP Host 1 File application Digital library application Video application RRPMSP HHP Host 2

16. Fall 2009COSC 65016 Machinery (cont) Multiplexing and Demultiplexing (demux key) Encapsulation (header/body) RRPDataHHP Application program Application program Host 1Host 2 Data RRP Data HHP Data RRP Data HHP

17. Fall 2009COSC 65017 Internet Architecture Defined by Internet Engineering Task Force (IETF) Hourglass Design Application vs Application Protocol (FTP, HTTP) … FTPHTTPNV TFTP TCP UDP IP NET 1 2 n

18. Fall 2009COSC 65018 ISO Architecture Application Presentation Session Transport End host One or more nodes within the network Network Data link Physical Network Data link Physical Network Data link Physical Application Presentation Session Transport End host Network Data link Physical

19. Fall 2009COSC 65019 Performance Metrics Bandwidth (throughput) –data transmitted per time unit –link versus end-to-end –notation KB = 2 10 bytes Mbps = 10 6 bits per second Latency (delay) –time to send message from point A to point B –one-way versus round-trip time (RTT) –components Latency = Propagation + Transmit + Queue Propagation = Distance / c Transmit = Size / Bandwidth

20. Fall 2009COSC 65020 Bandwidth versus Latency Relative importance –1-byte: 1ms vs 100ms dominates 1Mbps vs 100Mbps –25MB: 1Mbps vs 100Mbps dominates 1ms vs 100ms Infinite bandwidth –RTT dominates Throughput = TransferSize / TransferTime TransferTime = RTT + 1/Bandwidth x TransferSize –1-MB file to 1-Gbps link as 1-KB packet to 1-Mbps link

21. Fall 2009COSC 65021 Delay x Bandwidth Product Amount of data “in flight” or “in the pipe” Usually relative to RTT Example: 100ms x 45Mbps = 560KB

22. Fall 2009COSC 65022 Socket API Creating a socket int socket(int domain, int type, int protocol) domain = PF_INET, PF_UNIX type = SOCK_STREAM, SOCK_DGRAM, SOCK_RAW Passive Open (on server) int bind(int socket, struct sockaddr *addr, int addr_len) int listen(int socket, int backlog) int accept(int socket, struct sockaddr *addr, int addr_len)

23. Fall 2009COSC 65023 Sockets (cont) Active Open (on client) int connect(int socket, struct sockaddr *addr, int addr_len) Sending/Receiving Messages int send(int socket, char *msg, int mlen, int flags) int recv(int socket, char *buf, int blen, int flags)